On November 27, 1903, Wilhelm Hauschild wrote a letter – signed by 107 of his fellow workers – to his employer, the Friedrich Bayer and Co., seeking the company\'s support in starting a sports club. The company agreed to support the initiative, and on July 1, 1904, Turn- und Spielverein Bayer 04 Leverkusen was founded.

On May 31, 1907, a separate football department was formed within the club. In the culture of sports in Germany at the time, there was significant animosity between gymnasts and other types of athletes. Eventually this contributed to a split within the club: on June 8, 1928, the footballers formed a separate association – Sportvereinigung Bayer 04 Leverkusen – that also included the handball and fistball players, athletics, and boxing, while the gymnasts carried on as TuS Bayer 04 Leverkusen. SV Bayer 04 Leverkusen took with them the club\'s traditional colours of red and black, with the gymnasts adopting blue and yellow.

Through this period, and into the 1930s, SV Bayer 04 Leverkusen played third and fourth division football. In 1936, they earned promotion to the second highest class of play of the period. That was also the year that the club wore the familiar 'Bayer' cross for the first time. They made their first appearance in upper league play in 1951, in the Oberliga West and played there until 1956, after which they were relegated. SV Bayer 04 Leverkusen would not return to the upper leagues until 1962, just one season before the formation of Germany\'s new professional league, the Bundesliga. The next year saw the club in the Regionalliga West, tier II, where their performances over the next few seasons left them well down the league table.

SV Bayer 04 Leverkusen made something of a breakthrough in 1968, by winning the division title. Four years later, the team handily secured a place in the Bundesliga to start to play there in the 1979-80 season. By the mid-1980s, SV Bayer 04 Leverkusen had played their way into the upper half of the league table and were well-established there by the end of the decade. The new club took red and white as their colours. In addition to becoming an established Bundesliga side, the club earned its first honours with a dramatic win in the 1988 UEFA Cup. The club captured its next honours in 1993, with a 1-0 win in the German Cup over a surprising Hertha Berlin amateur squad.

After a near disaster in 1996 when the club faced a relegation battle, Bayer Leverkusen established itself as a powerful side, offering a technically pleasing offensive style of play under new coach Christoph Daum, who was also helped by the signing of players such as Lúcio, Emerson, Zé Roberto, and Michael Ballack. Daum was later to be famously fired for a cocaine scandal that also cost him his ascent to the role of the national team coach.